This invention relates in general to an improvement in wood burning stoves and in particular it relates to a method and apparatus for increasing the efficiency and safety of wood burning stoves.
Due to the relative scarcity and high cost of petroleum products, wood burning stoves have been increasingly employed for home heating and other purposes. A reasonably air tight wood burning stove is far more efficient than a home fireplace, which may result, in fact, in a net energy loss. However, wood burning stoves presently being utilized suffer from three significant drawbacks. First, wood burning stoves represent a severe fire hazard since the wood fuel therefore contains volatible substances which are normally not oxidized during combustion. These volatiles will burn if mixed with air at temperatures in excess of 590.degree. C. However, the typical wood burning stove operates within a temperature range of between 230.degree. and 370.degree. C. At these temperatures, these volatible substances, known generally as creosote, remain unoxidized and tend to adhere to the flue pipes and are a cause of not infrequent chimney fires. Secondly, the incomplete combustion of the carbonaceous fuel in wood burning stoves leaves the unoxidized residue as a pollutant and an environmental hazard which is discharged to the atmosphere. Third, the unoxidized residue represents a loss of overall combustion efficiency. While claims have been made to efficiencies greater than 65% in some wood burning stoves, independent testing laboratories have determined that the combustion efficiency of typical wood burning stoves lies in the range of between 50 and 65%. One possible solution to the aforementioned problems is to increase the combustion temperature of the typical wood burning stove by providing additional air into the combustion chamber so as to create temperatures high enough to bring about complete combustion. Variations on this technique date back to the 18th century with the Franklin stove, wherein the volatiles are mixed with additional air in the combustion chamber in order that temperatures high enough to bring about complete combustion may be obtained. These efforts have only been partially successful.
In application Ser. No. 173,155, filed July 28, 1980, by Van Dewoestine which is assigned to the assignee of the present invention, an improved wood burning stove is disclosed which obviates the foregoing problems. The wood burning stove disclosed therein employs a catalytic converter means which oxidizes oxidizable species in the exhaust from a standard wood burning stove. A wood burning stove modified to include a catalytic converter means provides increased safety due to the removal of creosote from the exhaust therefrom. Secondly, the wood burning stove disclosed by Van Dewoestine reduces unoxidized carbonaceous pollutants emitted from the stove. Thirdly, the improved wood burning stove disclosed by Van Dewoestine provides improved fuel efficiency through the use of the catalytic converter means.
However, it has been found that during startup and also once combustion is started and during the addition of fuel to the wood burning stove disclosed by Van Dewoestine, the impedance to the exhaust emanating from the stove caused by the catalytic converter means is detrimental. Specifically, it has been found that when the stove is opened, such as for example, when adding additional fuel, back pressure caused by the catalytic converter becomes excessive such that smoke and soot may emanate from the opening to the stove and may be expelled into the room being heated.
One prior arrangement for overcoming this problem is the bypass damper means for selectively closing the bypass as disclosed in the copending application Ser. No. 136,687, filed Apr. 2, 1980, by Albertsen, which is assigned to the assignee of the present invention.